Not Applicable.
This invention relates to eye surgery machines and in particular, for surgery machine finding application in ophthalmic operations. While the invention is described with particular emphasis in the use of the invention in cataract surgery, those skilled in the art will recognize the wider applicability of the inventive principles discussed hereinafter.
A cataract is the lens of the eye after it has become cloudy. Surgery to remove cataracts has been preformed for many years. Current practice is to remove the cataract by phacoemulsification, replacing the lens with an artificial one. Phacoemulsification utilizes a tube, usually referred to as an ultrasonic needle that is vibrated at ultrasonic frequencies to break up or emulsify the cataract. The needle is driven by a multi-function ultrasound handpiece. The handpiece conventionally includes an ultrasonic motor and fluid channels for aspiration and irrigation of the eye. Aspiration is used to evacuate the lens and other vitreous material from the eye. Irrigation replaces the volume removed by aspiration.
It is vitally important to maintain the intraocular pressure at an appropriate level during ophthalmic operations, by controlling the irrigation and aspiration capacity, thus preventing, in particular, the cornea from collapsing. Corneal collapse occurs when the system fails to supply sufficient inflow to the eye that compensates for the aspirated amount of liquid and/or tissue being removed, so that the device creates a vacuum within the eye itself.
In the past, a bag or bottle is normally used to store irrigation fluid. The fluid is connected to the ultrasound handpiece through flexible surgical tubing. The fluid is delivered to the handpiece under pressure, relative to the surrounding atmosphere. The pressure is developed either by gravity, i.e., hanging the bottle at an elevation greater than the handpiece, by pressurizing the bottle with air, or by using a pumping mechanism, for example. Ultrasound handpieces conventionally have a coaxial fluid flow design along the instrument tip. An irrigation sleeve surrounds the ultrasound needle. The sleeve is normally constructed from a pliable material, for example, silicone and rubber, which is intended to conform somewhat to the shape of the incision in the eye, thereby reducing wound leakage. A connection is made at the handpiece, between the irrigation sleeve and the tubing from the bottle. Fluid enters the eye through ports near the end of the sleeve.
Fluid and tissue are aspirated from the eye through a channel located inside the ultrasound needle. The channel through the ultrasound needle is in fluid communication with a connection on the back of the handpiece. Conventionally, flexible surgical tubing is connected to the handpiece at one end and to the surgery machine at the other end. Vacuum for aspiration is supplied to the tubing by the surgery machine. Surgery machines use various methods for controlling the vacuum level provided for aspiration. They also use various methods for storing the spent fluid and tissue.
During an eye operation, ideally pressure within the eye is maintained at a constant level regardless of fluid flow changes or wound leakage. In practice, pressure can vary a great deal, depending on fluid flow dynamics. One cause for pressure changes is the position of the eye in the fluid flow path. Conventionally, fluid flow restrictions exist between the fluid source, i.e., the irrigation bottle, and the eye. Fluid flow restrictions also exist between the eye and the vacuum or aspiration source. These restrictions cause a pressure drop, which is proportional to fluid flow, as fluid flows from the fluid source through the eye and to the vacuum source. As will be appreciated by those skilled in the art, as fluid flow increases, the pressure inside the eye decreases, it being assumed the fluid pressure at the bottle is a constant.
An additional cause for pressure change is the elastic nature of the tubing connecting the eye to the vacuum source. The diameter of the tubing changes, based on the pressure difference between the inside of the tubing and atmospheric pressure. That is to say, the tubing becomes smaller as vacuum increases. These diameter changes cause the tubing to store energy, damping pressure changes in the tubing. Often during surgery, the tip of the ultrasound needle becomes occluded. With occlusion, the pressure in the anterior chamber of the eye equalizes to the pressure of the fluid source and the pressure inside the ultrasonic needle approaches that of the vacuum source. When the occlusion breaks suddenly, the energy stored in the aspirating tubing causes a surge of fluid to flow, as the tubing returns to the size it was before the occlusion. The flow surge causes the pressure in the anterior chamber of the eye to decrease to a point lower than it would be under constant flow conditions. While this pressure change is momentary, it can be great enough to cause the pressure in the anterior chamber to be less than atmospheric pressure, causing the chamber to collapse.
In addition, any air in the aspiration tubing can exacerbate the pressure problem during surgery. Air bubbles can form from cavitation caused by the ultrasound needle, or from inadequate purging of the aspiration tubing during set up. Because of the compressible nature of air, the bubbles expand under vacuum, then contract as the vacuum is reduced.
Procedurally, fluid flow through the anterior chamber of the eye is used to manipulate tissue within the anterior chamber. As fluid moves, it tends to push items, for example lens material, membranes, and other undesirable debris, towards the tip of the ultrasound needle. To an observer, it appears as if the tip of the needle attracts material toward it. At very low flow rates, the attraction is small, and only things that are close to the tip move towards it. As the fluid flow rate increases, the apparent attraction is greater. At high flow rates, anything in the anterior chamber that is free to move is attracted to the tip of the ultrasound needle. The surgeon takes advantage of this tendency, because the tendency allows the ultrasound tip of the handpiece to remain near the middle of the anterior chamber most of the time, yet provides access to the tissues necessary to accomplish the surgery. The middle of the anterior chamber of the eye generally is considered a safer place to operate, reducing the likelihood of complications from the surgery.
In counter distinction to the attraction discussed above, as ultrasound energy, used to emulsify the lens, is increased, the needle tip tends to push the material intended for emulsification away from the needle tip. This push is greater with higher amounts of ultrasonic energy. However, a higher or greater amount of ultrasound energy is required to emulsify denser harder lenses than is required to emulsify softer lenses. In order to allow efficient transfer of energy to the lens, the lens must be kept against the needle tip. However, when the lens is positioned against the tip of the ultrasound needle, the lens tends to occlude the tip. The pressure difference develops across the lens, forming a holding force against the needle tip. The vacuum level at its source, the irrigation pressure, and the ultrasound needle inside diameter determines the maximum amount of force available to hold the lens. Aspiration assisted phacoemulsification occurs when the holding force generated by the fluid is much greater than that necessary to overcome the opposite push of the ultrasonic source. High vacuum causes stress in the lens to be higher, reducing or eliminating the need for higher ultrasound power to emulsify the lens. I am aware of medical studies that have shown a correlation between total ultrasound power used in phacoemulsification, and cornea endothelial cell loss. Because endothelial cells are not replaced by the body, the loss of the cells can be a serious surgical complication.
In general, the source of vacuum for aspiration when used for phacoemulsification can be provided in various forms. One form is a peristaltic pump, the operation of which causes the pump to act as a constant flow pump. That is to say, a vacuum developed by the pump increases with resistance to flow. An alternative source for vacuum for aspiration is a constant vacuum source. An example of a constant vacuum source is a venturi pump. A venturi pump is virtually insensitive to changes in flow resistance. There are then, generally speaking, two broad classes of surgery machines, one is the constant vacuum source and other is the constant flow source. Regardless of the type, however, phacoemulsification procedures performed with either machine work on the attraction/repulsion operation of the fluid and ultrasonic power described above.
Adjusting the different function valves of the surgery machine for ophthalmic procedures is a balancing act involving many factors influencing the adjustment. Maintenance of the pressure in the anterior chamber of the eye is the controlling factor. However, the maximum pressure allowed in the anterior chamber determines the maximum pressure setting for irrigation and the maximum flow rate available for irrigation. The aspiration flow setting is determined by the desired amount of attraction to the ultrasound needle. The density of the lens, coupled with a desire to complete surgery in the shortest possible time, affect the desired amount of ultrasonic power. The amount of ultrasonic power utilized, coupled with the inside diameter of the ultrasound needle determine the desired maximum vacuum setting. A change in any of the component characteristics used in the procedure can result in changing the usable ranges of all of the function adjustments.
As phacoemulsification surgery has increased in popularity, a number of solutions intended to control the pressure in the anterior chamber of the eye during surgery have been proposed. For example, the U.S. Pat. No. 5,766,146, describes a method of controlling the irrigation flow rate by using multiple irrigation sources. U.S. Pat. No. 5,810,765, also describes a method of controlling the irrigation flow rate by either changing the irrigation bottle pressure or connecting multiple irrigation bottles which differ in height, to the eye. U.S. Pat. No. 3,902,495, describes a device which vents automatically to reduce the vacuum in the aspiration tubing if the vacuum exceeds a preset limit. U.S. Pat. No. 4,935,005 (""005), describes a surgeon controlled connection of the aspiration tubing and the irrigation tubing to enable the surgeon to release access vacuum and equalize the pressure. The ""005 patent also describes a structure for blocking the aspiration tubing when a preset vacuum limit is exceeded. U.S. Pat. No. 3,693,613, describes using a vent to reduce vacuum automatically in the aspiration tubing if a sudden increase of flow in the aspiration tubing is sensed by the surgery machine. U.S. Pat. No. 4,494,342, describes connecting the irrigation tubing to the aspiration tubing automatically if a sudden increase in flow is sensed in the aspiration tubing. U.S. Pat. No. 5,569,188, proposes temporarily reversing the peristaltic pump, while U.S. Pat. No. 5,649,904, describes using a reflex mechanism in the aspiration tubing to reduce flow surge. U.S. Pat. No. 5,733,256, uses sensors near the ultrasound handpiece to reduce reaction time to changes in flow or pressure. U.S. Pat. No. 5,160,367, describes using a section of elastic tubing in the aspiration flow line, which has the effect of damping the post occlusion flow surge. U.S. Pat. No. 5,476,448, describes a device attached to the aspiration tubing that includes an elastic dome that collapses under increase vacuum, blocking the aspiration tube. The elastic dome returns to normal after the occlusion is cleared. U.S. Pat. No. 5,725,495, discloses a valve that squeezes the aspiration tubing to occlude aspiration flow rate. The valve is automatically controlled by the surgery machine. European Patent Application. No. 0 862902 describes a dome shaped plastic membrane which is connected into the irrigation line. The membrane forms a reservoir and dampens irrigation pressure changes. This wide body of art proposing solutions to the problems with eye surgery machines used in actual practice demonstrates that there is still a need for a device to prevent post occlusion flow surges during eye surgery.
It is therefore, one of the objects of this invention to provide a device by which high maximum aspiration vacuum level may be obtained without experiencing significant post occlusion flow surges during eye surgery.
It is another object of this invention is to provide a device that allows the use of higher maximum aspiration vacuum levels in combination with normal or large bore ultrasonic needles without experiencing significant post occlusion flow surges during eye surgery.
It is another object of this invention to provide a device to prevent post occlusion flow surges during eye surgery which is tolerant to air bubbles in the aspiration tubing.
Another object of this invention is to provide a device for reducing the amount of ultrasound energy necessary to dissassemble a cataract by use of high vacuum aspiration without experiencing a significant post occlusion flow surge during eye surgery.
Yet another object of this invention is to provide a device which allows a constant vacuum source to be used for aspiration during phacoemulsification surgery without performance compromises when compared to a constant flow vacuum source.
Another object of this invention to provide a device which maybe employed effectively with both constant vacuum and constant flow surgery machines and instruments that are currently in use.
Another object of this invention is to provide a relatively low cost, device for preventing post occlusion flow surges.
Yet another object of this invention to provide a disposable device for prevent post occlusion flow surges during eye surgery.
Other objects of this invention will be apparent to those skilled in the art in light of the following description and accompanying drawings.
In accordance with this invention, generally stated, a device is inserted along the aspirating line of an eye surgery machine. The machine includes a handpiece for performing eye surgery. Preferably the device of the present invention is attached in the aspirating line at the handpiece. The device includes an enclosure having an inlet and an outlet. A flow passage extends between the inlet and the outlet. In the preferred embodiment, the inlet of the device is attached to the handpiece and the outlet of the device is attached to the vacuum line of the surgery machine. The device includes a restriction in the flow path of the device, which defines a flow limit for aspirated fluids. A filter is positioned in the flow path upstream of the restriction. The device enclosure has a predetermined storage capacity for retaining material blocked by the filter. The preferred embodiment further includes a second passage in the enclosure between the filter and a point downstream of the restriction for permitting passage of air bubbles, for example, which sometimes enter the aspirating stream during surgery.